TL;DR the reservation system is absolutely unreliable, and without the Uber Pass, is just not worth it.
I’ve been using JUMP bikes and scooters with the Uber Pass for a few months now, and the free 30 minutes a day absolutely made it worth it for me. There were a couple of issues though. Frequently I would encounter bikes with non-working e-assists. Even more annoying though, I would go up to bikes and scooters (I would check that they were available on the app), try to reserve them, and get hit with mysterious errors that they weren’t reservable. The issues seemed to have gone away over time.